1. Th Loarer - SEWG on Fuel retention – JET, 22-23 July 2008 1 Th Loarer with special thanks to S Brezinsek, J Bucalossi, I Coffey, G Esser, S Gruenhagen Ph Morgan, V Philipps, R Stagg, J Strachan. And also EU TF on PWI and JET EFDA contributors Fuel retention in JET Recent results in L and H-mode

2. Th Loarer - SEWG on Fuel retention – JET, 22-23 July 2008 2 OUTLINE Recent results in - L mode - Type I ELMy H-mode Retention - Implantation - Co-deposition: correlation carbon source - EDGE2D Further plan

3. Th Loarer - SEWG on Fuel retention – JET, 22-23 July 2008 3 Introduction - Reference in carbon before moving to a full metallic wall: Quantify the benefit (?) - Validation of the method - Can we avoid the regeneration? - Gas balance on line for each discharge? - DT experiments (JET and TFTR) remain very good references for - Gas balance - Post mortem - Fuel removal - Comparison with other devices: AUG, JT-60U, but also limiter devices - Extrapolation to ITER

4. Th Loarer - SEWG on Fuel retention – JET, 22-23 July 2008 4 Calibrated Particle Source (Gas, NBI…) Divertor cryo-pumps Wall Retention Long & Short Term Gas balance procedure on JET Repeat sets of identical discharges (no intershot conditioning) to avoid history effects Plasma Injection = Pumped + Short Term Ret + Long Term Ret Total recovered from cryo-regeneration: Pumped + intershot outgassing over ~800s (assumed equal to Short Term Ret ) Regenerate cryopumps before and after expt. collect total pumped gas (accuracy~1.2%) Dedicated series of experiments: L and H mode in 2007-2008 as ref for ILW

5. Th Loarer - SEWG on Fuel retention – JET, 22-23 July 2008 5 8 repetitive pulses I p /B T =2.0MA/2.4T, 1.8MW ICRH only (42MHz) All auxiliary pumps (NBI, LH, main Turbo pumps) off Regeneration of divertor cryopump before and after session Long Term retention Injected – Regenerated (regeneration about 60 min after last shot) L mode: short limiter phase L-mode, HT3 with ~1.7x10 22 Ds -1 and Early X-point formation Recent session Evaluate the contribution of the limiter phase

6. Th Loarer - SEWG on Fuel retention – JET, 22-23 July 2008 6 HT3 – Mode B (early X-point) and D -Mode D standard X- point (~9s of limiter start-up phase) # 70534 - Mode B: Early X- point (~1.3s of limiter start-up phase) # 73654 Except the limiter phase Comparable plasma parameters I p, B T, n e, ICRH, Gas rate, recycling… Ip ne ICRH Gas rate Total injected H Limiter phase I p /B T =2.0MA/2.4T, 1.8MW ICRH only

7. Th Loarer - SEWG on Fuel retention – JET, 22-23 July 2008 7 Heating and gas injection ~ 75 s (8 pulses) – Mode B (8 th July 2008) Total divertor time: ~ 170 s, Total limiter time: ~10s Injection: 24.761 Barl 1.22 10 24 D-atoms Total recovered 21.02 Barl 1.03 10 24 D-atoms Retention 3.741 Barl 1.84 10 23 D-atoms (~15%) Comparison of L-mode experiments Heating and gas injection ~ 81 s (6 pulses) – Mode D (March 2007) Total divertor time: ~ 126 s, Total limiter time: ~60 s Injection: 27.882 Barl 1.377 10 24 D-atoms Total recovered 24.454 Barl 1.208 10 24 D-atoms Retention 3.428 Barl 1.693 10 23 D-atoms (~12%) Detailed analysis of ramp-up and ramp-down phase in progress

8. Th Loarer - SEWG on Fuel retention – JET, 22-23 July 2008 8 Retention in L and H-mode Pulse type Injection (Ds -1 ) Heating phase (s) Long term retention (Ds -1 ) Divertor phase (s) Long term retention (Ds -1 ) L-mode Mode D ~1.8 10 22 81 2.04 10 21 126 1.27 10 21 L-mode Mode B ~1.7 10 22 75 2.40 10 21 170 1.05 10 21 Type III ~1.7 10 22 72 2.40 10 21 126 1.37 10 21 Type I~1.7 10 22 322.83 10 21 501.7 10 21 Impact of the limiter phase in the fuel retention experiments with an early X-point (~1.2s of limiter phase) and late X-point formation (~8-10 s of limiter phase) is moderate. Normalisation Divertor vs. Heating time ! Consistent with the previous results, but divertor time and limiter time difficult to evaluate with accuracy. Retention closely linked to the carbon source

9. Th Loarer - SEWG on Fuel retention – JET, 22-23 July 2008 9 Type I ELMy H-mode n e ~0.7n GW P TOT (MW) NBI+ICRH~13MW D (in) D (out) Time (s) #69260 I p = 2.0 MA, B = 2.4 T - Short term retention : limited to fast reservoir and recovered in between pulses (outgasing) - Long term retention : Co-deposition and implantation : Slow process compared to short term over 5-10 sec W ELM ~100 kJ ~ 60 Hz Heating phase Injection Exhausted Retention

10. Th Loarer - SEWG on Fuel retention – JET, 22-23 July 2008 10 High power discharge in JET I p =3.5MA, B T =3.2T nene P tot (NBI + ICRH) ~ 23-24MW W dia ~9.5MJ Gas: 5.0x10 22 Ds -1 ELMs 600-700kJ per ELM Gas balance on line, w/o regeneration

11. Th Loarer - SEWG on Fuel retention – JET, 22-23 July 2008 11 Gas balance High power discharge Using the same pumping speed Retention as high as ~3.3x10 22 Ds -1 Consistent with strong carbon erosion from recycling and ELMs Increase by ~10 of the retention To be confirmed by dedicated exp

12. Th Loarer - SEWG on Fuel retention – JET, 22-23 July 2008 12 C source for High power discharge Type I ELMs (600-700kJ) L mode Type I ELMs (100kJ)

13. Th Loarer - SEWG on Fuel retention – JET, 22-23 July 2008 13 Carbon production and scenario J Strachan et al. Nuc. Fus. 2003 L mode (3-4MW) Type I H mode 10-15MW - Increase of carbon source depends on scenario (ELMs, recycling flux…) enhanced retention by co-deposition - Increase by a factor of ~2 of carbon source from L to type I ELMy H-Mode

14. Th Loarer - SEWG on Fuel retention – JET, 22-23 July 2008 14 Carbon production and scenario J Strachan et al. PSI 2008 Carbon ionisation rate in the SOL as a function of D ionisation rate

15. Th Loarer - SEWG on Fuel retention – JET, 22-23 July 2008 15 D,T Wall Mechanisms for fuel retention Two basic mechanisms for Long term fuel retention Deep Implantation, Diffusion/Migration, Trapping C, Be C, Be, D,T Codeposition Short term retention (Adsorption: dynamic retention) ~ Recovered by outgassing Separate the contribution of implantation and co-deposition?

16. Th Loarer - SEWG on Fuel retention – JET, 22-23 July 2008 16 DT experiments in JET Retention by implantation and co-deposition Same retention although different scenario TFTR Phase 1 (June 1997) Gas injection only 11.4g 2.34x10 24 T injected 1.0x10 24 T retained (~40%) 80 pulses in L mode Phase 1 Phase 2 (End 1997-Early 1998) Both NBI and Gas injection 23g ~40% retained High power discharges in H mode Phase 2

17. Th Loarer - SEWG on Fuel retention – JET, 22-23 July 2008 17 Implantation and co-deposition 50-50% D/T100% T Early phase of DT experiments Retention~100% for the 10 first discharges (~4x10 23 T) Retention deduced from Cryo regeneration Injection

18. Th Loarer - SEWG on Fuel retention – JET, 22-23 July 2008 18 Implantation JET DT experiments - Implantation dominates in phase 1 - Co-deposition main process in phase 2 - JET ~ 200 m 2 : maximum retained fluence ~10 21 m -2 reservoir of ~ 2 10 23 T consistent with implantation of particles with incident energy of ~ 200eV.

19. Th Loarer - SEWG on Fuel retention – JET, 22-23 July 2008 19 Summary…and further plans! - No impact of the limiter phase in the gas balance analysis - Retention linked to carbon production - Implantation Dominant process in early phases Later co-deposition - Further plans Dedicated session with high power (ELMs) /injection - Modelling correlate the retention with carbon source (EDGE2D)

20. Th Loarer - SEWG on Fuel retention – JET, 22-23 July 2008 20 Retention: Short and long term Short term retention - Depends on plasma scenario, wall conditioning and Material (Be, C)… -Limited to fast reservoir and recovered in between pulses (outgassing) Actively cooled device Steady state operation-->Long term retention Long term retention - Co-deposition Correlated to C production - Implantation Edge plasma, material structure… Dynamic retention: 5 x10 21 D JET 2.5 10 22 D ~ wall area ratio

21. Th Loarer - SEWG on Fuel retention – JET, 22-23 July 2008 21 Gas Balance (1/2) From cryo-pump regeneration (~1%) and calibrated gas injection Evaluation of the pumped flux - During the plasma - Between pulses 0 10 100 1000 10000 1min 1hour1day1week Plasma During plasma inj > pump Retention>0 Short & Long term Between pulses, session, days… inj =0 pump = Outgasing Retention<0 Short term retention only (dynamic retention) Evaluation of Short and Long term retention Injection = Long Term Ret + Short Term Ret + Pumped flux

22. Th Loarer - SEWG on Fuel retention – JET, 22-23 July 2008 22 Gas balance (2/2) Two complementary methods to measure the pumped flux 2 – Collection of all the total particles pumped (Tbo, Cryo…) into a separate calibrated volume (equivalent to the AGHS used at JET) - Accurate neutral pressure measurement in volume (Temperature) - Analysis of the gas composition collected (H, D, T and Impurities) 1 – Neutral pressure and Pumping speed Pumped flux = P Div *S Div + P NBI * S NBI + P Diag *S Diag - Require enough pressure gauges located in the pumping pipes, regular calibration of both pressure gauges and pumping speeds. - These 2 methods are complementary; the second method gives the equivalent of the integral of the first one. - Allow to check/limit/evaluate the possible drift of the neutral pressure measurements over long periods (days, weeks…). - These two methods are technically easy to be implemented.